Quantitative Assay for the Direct Comparison of Platinum Catalysts in Benzene H/D Exchange

Abstract

This paper describes a protocol for the direct comparison of diverse Pt catalysts in the H/D exchange between C 6 H 6 and TFA-d 1 , CD 3 CO 2 D, and TFE-d 3 using turnover number (TON) as a standard metric. An initial survey of Pt complexes, including commercial Pt salts (PtCl 2 , K 2 PtCl 4 ) and Pt chloride complexes containing bidentate and tridentate nitrogen donor ligands, has been conducted. These studies have established that the addition of AgOAc (in TFA-d 1 ) or AgBF 4 (in CD 3 CO 2 D and TFE-d 3 ) displaces the Cl ligands on the Pt precatalyst, which leads to dramatically increased turnover numbers. In general, PtCl 2 and K 2 PtCl 4 provided the fewest turnovers, and species containing bidentate ligands afforded higher turnover numbers than those with tridentate ligands. A diimine Pt complex was found to be a top performing catalyst for H/D exchange with all deuterium sources examined. Interestingly, the relative reactivity of many of the catalysts varied dramatically upon changing the deuterium source, highlighting the need to thoroughly assay potential catalysts under a variety of conditions.

Platinum and Palladium Complexes Containing Cationic Ligands as Catalysts for Arene H/D Exchange and Oxidation

“…The catalysts were also compared on the basis of turnover numbers (TONs). Complexes 3 a – c achieved the statistical maximum TON of 242 after 24 hours,11, 12 which is also superior to the results with [dtbpyPtCl 2 ], [dtbpyPdCl 2 ], and 1 (TON=144±12, 90±18, and 94±13 under analogous conditions) 10d. Lowering the catalyst loading of 3 a to 0.1 mol % resulted in turnovers of 3273±110 after 48 hours at 150 °C, which demonstrates the high activity and stability of this species, even upon prolonged heating at elevated temperatures.…”

“…We first evaluated 3 a – c as catalysts for H/D exchange10 between [D 4 ]acetic acid and benzene using an assay developed in our laboratory 10d. Under our standard conditions, (2 mol % [M], 4 mol % AgBF 4 , 1 equiv C 6 H 6 in 25 equiv of [D 4 ]AcOH, 150 °C), these complexes showed very high catalytic activity, with turnover frequencies (TOFs) of 0.1 s −1 ( 3 a , b ) and 0.05 s −1 ( 3 c ) after 15 minutes at 150 °C.…”

“…Under our standard conditions, (2 mol % [M], 4 mol % AgBF 4 , 1 equiv C 6 H 6 in 25 equiv of [D 4 ]AcOH, 150 °C), these complexes showed very high catalytic activity, with turnover frequencies (TOFs) of 0.1 s −1 ( 3 a , b ) and 0.05 s −1 ( 3 c ) after 15 minutes at 150 °C. For comparison, [dtbpyPtCl 2 ] (dtbpy=4,4′‐di‐ tert ‐butylbipyridine), [dtbpyPdCl 2 ], and bipyrimidine catalyst 1 provided TOFs of 0.0002, 0.002, and 0.003 s −1 , respectively, under identical conditions 10d. The catalysts were also compared on the basis of turnover numbers (TONs).…”

C−H Functionalisation for Hydrogen Isotope Exchange

“…Indeed, this was the case in the earlier of Sanford's aforementioned deuterium labeling studies, where cationic bipyridine ligands were employed to produce advantageously Lewis acidic catalysts, 65 and 66 (versus 64), for the deuterium labeling of benzene in the presence of CD3CO2D (Scheme 26). [110,111,112] Although both metals produced highly active HIE catalysts compared to the parent catalyst of the study (64), Pt was more useful than Pd, as Pt provided the most highly acidic catalyst.…”

Catalytic CH Bond Activation at Nanoscale Lewis Acidic Aluminium Fluorides: H/D Exchange Reactions at Aromatic and Aliphatic Hydrocarbons

“…H/D exchange processes are frequently performed with deuterium sources such as [D 6 ]benzene or [D 6 ]acetone, deuterated alcohols and in some cases with deuterium oxide. [1,3,[6][7][8][14][15][16][17][18] To achieve a hydrogen/deuterium exchange at C À H/D bonds under mild conditions, powerful molecular or nanoscale catalyst materials are usually required. [16,17,[19][20][21][22][23][24][25] For effective conversions often precious and expensive transition-metal catalysts, such as organometallic complexes, metal nanoparticles or metals on carbon or alumina support, are needed.…”